Abstract
Undercooling of low melting point metals, Sn and In, on graphite, Cu, and Au-coated Cu surfaces is examined using an in-situ x-ray diffraction technique. Undercoolings of up to 56.1ºC were observed for Sn solidified on graphite, which is a non-wetting substrate, while lower undercoolings were observed for Sn of 17.3ºC on Au/Ni/Cu and 10.5ºC on Cu surfaces. Indium behaved quite differently, showing undercoolings of less than 4ºC on all three substrates. In addition, lattice expansion/contraction behavior of Sn, In and intermetallic compounds (IMCs) that formed during the reaction of Sn with the Au/Ni/Cu surface were measured. Results showed anisotropic and non-linear expansion of both Sn and In, with a contraction, rather than expansion, of the basal planes of In during heating. The principal IMC that formed between Sn and the Au/Ni/Cu surface was characterized as CuSn and had an average expansion coefficient of 13.6x10-6/°C, which is less than that of Sn or Cu.
